The present invention relates to the field of information transmission and more particularly to a secondary information transmission system such as a monitoring and/or regulating or control system adapted to be coupled in an information transmission system transparent to the information transformation system. In particular, the present invention has application to telephone systems whereby telephone lines are used by the secondary system to continuously transmit information without disturbing normal communications on the telephone lines.
It would be highly desireable to utilize an information transmission system (sometimes hereinafter referred to as a primary system), particularly an existing system such as a telephone system or an intercom system, to name two, for transmitting additional information without disturbing normal information transmission of the system. The information transmission system could then be used to monitor one or more conditions at one or more locations in the information transmission system, and transmit condition information to a remote location which could be an intermediate or central location in the information transmission system, while the system carries out its primary information transmission function. Conditions which can be monitored might include, for example, temperature, light, smoke and the presence of an intruder at the monitored location. It would be further desireable if the primary information transmisson system could be used for two-way secondary information transfer. In such a case, not only could a condition be monitored at a location in the primary information transfer systems, but also apparatus could be controlled in response to the monitored condition from the remote location. For example, temperature could be monitored and heating or cooling apparatus could be controlled, or light could be regulated and lighting apparatus controlled.